def get_statistic(region, indicator="总人口"):
    if region == "呼和浩特市":
        hohhot_data = {"总人口": 289.7}
        return hohhot_data.get(indicator, None)
    elif region == "包头市":
        baotou_data = {"GDP": 3000}
        return baotou_data.get(indicator, None)

    return None


# 由于indicator的默认值为"总人口"
# 因此查询"总人口"数据时无需传递实参
print(get_statistic("呼和浩特市"))
# 覆盖默认值，查询"GDP"
print(get_statistic("呼和浩特市", "GDP"))
